The present invention relates to cost control management in telecommunication systems and more particularly to cost control management in mobile telecommunication systems.
In today's mobile telecommunications networks, the operator of a mobile network is able to maintain tight control over the calls made and services used by its subscribers when they are at home, i.e. when they are registered with the operator's own network. For example, if a subscriber exceeds his calling credit limit the operator can notify the subscriber of this situation and/or can prevent the subscriber from making further calls until his outstanding account is settled. Similarly, where a subscriber makes use of a top-up account, e.g. using scratch cards to credit his account, an operator can restrict the subscriber's access when the subscriber's credit drops to zero. Such charging control is possible because of the introduction into mobile networks of Intelligent Network (IN) nodes which use the so-called Intelligent Network Application Part (INAP) protocol to communicate with one another. For example, a Service Switching Function (SSF) associated with a serving MSC or Gateway MSC (GMSC) of a GSM network may exchange charging information with a Cost Control Function (CCF) using INAP.
IN/INAP enables an MSC or GMSC to send charging information at regular intervals to a charging node of a subscriber's home network. However, this is only possible when the MSC/GMSC is present in the home network. In the event that a mobile subscriber is registered with an MSC/GMSC of a foreign network (i.e. the subscriber is “roaming”), Call Detail Records (CDRs) generated by the MSC/GMSC are passed to a home network through a clearing house in so-called TAP files (if necessary, multiple CDRs are collated in the foreign network and the collated CDRs are sent to the clearing house in a single TAP file). It can take at least two days or even more before the CDRs are forwarded on to the home network.
A home network cannot therefore monitor, in real time or near real time, the charges being incurred by one of its subscribers when that subscriber is roaming in a foreign network. Rather, charging information is only sent periodically from the foreign network to the home network (e.g. every few days). There therefore exists a possibility that fraud by a roaming subscriber will go undetected by the subscriber's home network for some time, and that during that time the home network operator will incur considerable losses. Furthermore, even though CDRs can be generated periodically for a subscriber when that subscriber is registered with his home network, the use of exchanges which generate CDRs at fixed regular intervals for all registered subscribers represents a non-optimal solution as the fixed interval may be too long for certain classes of subscribers and too short for others, and can unnecessarily increase the computational load in the serving exchange.
In order to overcome these problems, a mechanism referred to as Customised Applications for Mobile network Enhanced Logic (CAMEL) has been standardised by ETSI (further enhancements to CAMEL are in the process of being standardised—3GPP). CAMEL provides for the transfer of charging related information in near real time between a Service Control function (SCF) associated with a Cost Control Function (CCF) (the CCF is usually running at a Cost Control Node (CCN) located in a subscriber's home network) and a Service Switching Function (SSF) typically running at, or associated with, an MSC or GMSC (in the case of a GSM network). The SSF may be located in the same network as the CCF or in a different network. CAMEL enables an access control node to authorise a roaming subscriber for a fixed time period at the end of which the access control node must seek a new authorisation for the subscriber. It will be appreciated that one application of CAMEL is in respect of pre-paid subscribers. A protocol known as the CAMEL Application Part (CAP) protocol has been defined for the purpose of transporting CAMEL messages between a CCF and a SSF.